The present invention relates to a linear rolling guide device suitable for relatively small equipment including office automation and measuring equipment.
In the conventional design a linear motion rolling guide assembly has a rail and a slider, through the rolling of a plurality of rows of rolling elements, riding and sliding on the rail.
The slider includes a steel body with an elongation extending downwards on both sides of a steel plate. A plurality of pairs of longitudinally arranged grooves, provided as tracks of the rolling elements, are formed on inside faces of the elongation. A plurality of pairs of holes as return passages of the rolling elements is drilled through the elongation. Two end caps, including the turnaround channel, which connects the track of rolling elements and the return holes, are mounted on both end faces of the steel body by fixing screws.
The smaller the hole is, the more difficult it is to drill. To overcome the manufacturing difficulty designs of return hole, formed by an open groove and a closure, member are provided, see the U.S. Pat. No. 4,637,739, and European patents EP 0 494 682 A2 and EP 0 474 948 A1.
EP 0 494 682 A2 and EP 0 474 948 A1, taught an alternative design which simplifies the manufacture and mounting complexity.
In the EP 0 494 682 A2 the disclosed interlocking design by using a snapping means, which is integrally formed on the longitudinal end of the closure member of the return track, to fix two monolithically end caps with a return track. The space of the snap means is limited by the shape of the closure member, which is also constrained laterally by the mounting holes for the connection of the surrounding part designed to slide relative to the rail, and vertically by the fitting edge for the surrounding part. A firm interlocking of the snap means, especially for the small size linear rolling guide device, is difficult to achieve.
In DE 195 38 665 A1 another snapping design is disclosed. A casement enfold the bottom of the steel body and form the ball return tracks space in between, two end caps are inserted vertically from top into the axial space between the endplate of the casement and the end face of the steel body. These two end caps press the steel body down to the casement by the projection overhead and are fastened vertically on the casement by using a snapping mean on the endplate of the casement and the outside face of the end cap. The casement provides positioning surfaces for the steel body and the end caps, respectively. A disadvantage of this is the indirect positioning between the end caps and the steel body. This elnarges the misalignment between the return channel and the turn-around channels of the rolling elements and causes an unsatisfactory rolling element re-circulation.
The conventional and economical fabrication of the precision plastic injection molding can achieve an positioning and form accuracy of ca. .+-.0.02 mm relative to a length 0.5.about.1.5 mm; and the minimal fillet radius/chamfer can achieve an accuracy of 0.1 mm. Any higher accuracy requirement will substantially increase the manufacturing cost. Such inaccuracy and the minimum fillet limit the minimization of the linear motion rolling guide device. A firm and accurate interlocking is secured only if the fitting surfaces of the parts to be attached together are large enough and are precisely conformed to each other. The smaller the linear motion rolling guide device is, the smaller is the fitting surface. This also limits the maximum extent of minimization of the dimensions.